Method of making glass-metal seals



Sept' 20, 1949- w. J. KNocHEl. ETAL v 2,482,494

METHOD 0F MAKING GLASS-METAL SEALS Filed March 25, 1943 Si Oz i I Je o: M Pla Z 6m: A z J 7' iz 4 z 05 l 10 Y 14 l l do y INVENTORS BY n ATTORNEY atented Sept. 2Q, 1949 wUNI T1-:off STAT .METnoDloF MAKING GLA s's-ivnsfriiI'. SEALs William J. Knochel"and "Jens J. AakjeLj'East Orange, N. J., assignors to Westinghouse fElectric Corporation; `East Pittsburgh, Pa., aV oorporation of Pennsylvania Application March 23, 194s, serial Ne. 4350.166

, ZCIaims.

Our invention relates to'a method of making glass-to-metal seals such'as are used, for' in2- stance, 'in electronic'devices, sealed resistors or 'other structures which 'contain ametal body connected with or sealed to a body of glass or the like vitreous' 'Ir'iaterialV It is, 'as a rule, essential for a satisfactory permanent seal that the jmetal in immediate and sealing contact with the, vitric material have a coefficient of thermal expansion similar to that of the latter material, and it has become customary to provide special 'nickel-steels or nickelcobalt steels for this purpose. In particular, when using glass of the boron-silicate type for the envelopes of electronic discharge devices, a special steel alloy as 'described in Patent No. 2,062,335, issued December 1', 1936, to Howard VScott on aV Glassmetal seal, contains 28% to 34% nickel, 5% to 25% cobalt, less than 1% manganese, and less than 0.1% carbon. `A specie composition of this metal alloy, according to the patent, is formed'of 29.8% Ni, 15.5% Co, 0.22% Mnand less than 0.1% C, and has virtually the same coeicient of expansion (between 3.0 and 5.5X10-6 cm. per degree centigrade)v as glass composed of 73.8% S102, 0.5 A5203, 5.2% PbO, 1% A1203, and 18.7% B203. Q

,Thealloy metal part to be sealed to the glass must be cleaned and baked before glas'sing it in order to'obtain seals of satisfactory tightness and permanence. A treatment' of this kind includes normally the steps of degreasing the metal,l cleaning it with hydrochloric acid, and baking' it at 1000 to 1100 C. for approximatelyla half hour in la hydrogen atmosphere. After the treatment, the alloy parts are welded, soldered or brazed to other metal'parts of the assembly, then polished andmade ready -for the glassing operation. 1f possible, the degreasing and hydrogen baking steps are repeated before joiningthe alloy part to the glass bodyj by fusion. 1

There are cases, however, Wherea relatively long time elapses between the degreasing and baking steps and the final glassingv operation, or where these steps cannot be repeated after the alloy part has` once been assembled ywith the other metallic elements of the appertainingstructure. For instance, in various typesof electrode assemblies, such as the anode assembly of cer'- tain vX-ray tubes, a copper cable is 'joined with the alloy part by silver solder. Dueto the presence and proximity of copper and silver, the highl temper ture baking -cannotbe repeated without damagey to the assembly.' Underthe just-mentioned conditions ,the known sealing operationre- 2 Y suits often in unsatisfactory seals ras to stability and vacuum-tightness of the glass-to-metal joint.

It isarr object of our invention to providea` methodof -making glass-to-metal seals of the aforementioned kind,;which insures a satisfactory yseal '-regarclle ss of the length 'of time that intervened between Athe cleaning j and baking of Vthe alloy steel and the final glassing operation.y

Another object of the invention is to provide a glassng method for nickelsteelsiof the type here l'referredy to, which insures a'satisfactorypermanent seal in'cases Where la repetition of a cleaning and baking treatment isyinappropriate or unfavorable once the steel body has been assembled with other elements.

Still another'object of our invention, allied to the foregoing', is to provide vsimple'and effective means for'performing our glas'sing 'method' in the course of normal manufacture and with the aid o f normaal factory Vequipmentso asr tok avoidv an appreciable addition tofthe rtime and cost of the 'glassing procedure as, heretofore customary. 1i -We have discovered that the above-mentioned objectives and advantages are achieved, ifthe nickel steel or alloy parts previously cleaned and then lloakedat a temperature of 1000 and more degrees centigrade, `are made ready for glassing inf-ther customary manner, but are then heated for a short time at red heatin a reducingiatmospherejbeforethe glassing proper is performed. The temperature of the heating, immediately precedingthe nal glassing step, is approximately 900 'C,., i. e., below the vbaking temperature and not 4injurious tol any copperl or silver elements attached to theV steel part.v The heating timeis from vabout to 10 minutesfor instance,'approxi mately 5 minutes. [According Vto another 'feature of the "invention, the intermediate reducing heat treatment is'performed with the 'aid of burners operating with a hydrogen-,rich flame. It is also a'feature ofthe invention to useV for the reducing heating the same burners that serve subsequently for the glassing'operation proper and to vary the proportional supply offoxygengand'hydrogen to the burner in order to VVeffect the change from a reducing toi an oxidizing ,atmo'sphere.

The' invention will beqmore clearly understood from the following-description in conjunction with the drawing, m'fwhich: Y j 1- 1 Y A Figure'lrepresents al "teral partgsectional view of j'discharge device containing a glass-metal seal madefinfaccordance with the invention; Fig; 2 Villustrates the reducing heat treatment in accordanceiwith the invent/iones applied@ one of the glass-metal seals of the apparatus shown in Fig. 1;

Fig. 3 illustrates the next following method step, i. e. the nal sealing operation, as applied to the same part of the apparatus of Fig. 1; and

Fig. 4 shows a longitudinal .section .through the anode portion of an ,X-ray tubecontaining .a glass-metal seal made and treated in accordance with the present invention Referring to Fig. 1, reference numeral I designates the vacuum vessel or ienvelope'of afmercury arc discharge tube. The bottom .of the vessel is closed by a disc-shaped bottom ,plate-T2 covered by a pool 3 of mercury. The upperl end of the cylindrical Vessel I is closed by a. header 4 which carries the anode structure of the dischargeapparatus. The bottom plate 2 andthe h'eader are tightly sealed to the cylindrical wall :of the vessel I.

The anodestructuremounted on the header 4 includes the anode body proper marked by numeral 5. This body consists of .carbon and is .mounted on a stem 6 of copper or the likehighly conductive material. lA copper terminal 1V engages the stem 6 and is firmly soldered to the .stem by means ofA a silver solder located at the junction 8. The terminal 1 is connected to a braided copper cable 9 `serving to supply the `anode connector.

A vacuum-tight junction between the anode assembly and the header 4 .of the discharge vessel is formed of a cylindrical body I ofglass or the like vitreous material and of two intermediate metal bodies II and I2, also of .substantially .cylindrical shape which consists of a metal, such as theabove-mentioned alloy, whose thermal coefficient of expansion is similar to that of the glass body I0. "The metal body I2 has one of `its ends sealed vacuum-tight tothe stem S .b y welding, brazing or soldering; .the .other end at I3 is sealed 'to theV glass body I0 by fusion with the aid of the method according .tothe present invention. 'Thelower edge of the metal body I'I is 'similarly welded or otherwise joined with the headerf4, while the upper edge, at I4, 4forms a seal with the glass body IIl. .The latter `sealis also produced'bya method according to the Vinvention.

'When Vmanufacturing and assembling the discharge device, and particularly the header4 and the anode structure, the metal parts VII and `I2 are rst subjected to the so-called carburization schedule consisting of a degreasingstena following cleaning treatment .under .application of hydrochloric acid, and a next Afollowing ybaking treatment at a temperature of Y1000 .to .1100 C. for approximately a half hour ,in .a hydrogen atmosphere. This treatment isset forth in the Howard Scott Patent 2,043,307 of June 9, ,19.36.,

and is in accordance with the customary procedure mentioned in the foregoing and is carried out before the parts II and I2 are joined with the other metal and glass bodies of the Yanode assembly described below.

After joining vthe metal `body -II to the header it tion, as indicated by the arrow I8, and the abovementioned intermediate heat treatment is applied to the part of the sleeve I I to be joined with the glass body I0. This treatment is performed by applying a hydrogen-rich flame to the body .I I. To this .end, a number .of burners are arfranged substantially in ra'dial direction relative to the axis of rotation. One of lthese burners is indicated at I9. Another burner, extending perpendicularly to the plane of illustration, is indi- :cated at .20..1Theidame is produced by feeding amixture of oxygenand hydrogen to the burners.

'The .relative .amounts of oxygen and hydrogen --are.adjustable for."instance, by means of a regu- .lating valve :.(notillustrated). When performing the reducing heat treatment just mentioned,

"the'gas'supplyito-'the burners is so adjusted that the. hydrogen predominates, so that the reducing atmosphere within the body of flames surround- .ingthe sleeve 4ILI when performing .the treatment is'ricninhydrogen and has a reducing eect on the sleeve II and on any oxides formed on the metal r`surface 'to"be,`jo'ine`d with the `glass body. Thisheatingtreatment is maintained at a temperature of 850'to`930" C. orapproximately 900 C'. for aperiod `between 3 and'j10 minutes, A treatmentfor about`"5 minuteshas proved to be sufficientfor favorable results.

4lifter the termination of the .reducing heat treatment, 'the lsleeve .'III is ,permitted to cool. Then the treated portiono'f the sleeve II is polis'hediby applying alOxite cloth (320 grit). The Apart "I'I is'then wipe'dwith a clean rag that has been dipped in alcohol. After that, the part II 'isready'for the'finahglassing operation. It is not alwaysnecessary'to polish after the treatment.

".The final operation .requires heating both the edgeportion of sleeve 'I I andthe glass body I0 up tothefusion temperature. "For thispurpose, the supply of 4gas .to theseries ofLburners, including theiburners 1I9.and 20, is so adjusted that now the flame atmosphere `lsrich `in oxygen-and .correspondingly .low in hydrogen. This `produces the required atmosphere as well as'the' necessary. higher temperature. .At the .same time, another 'se'tof burners, represented'by the burner 2I,.is used for heatingtheglass cylinder 10. The tail .chuck 'I1 of the'latheis'kept in'rotation at the'sarne speed 'and in 4thesame direction (arrow r23) astheheadchuck I5, sothat no relative rotation :exists Abetween the 'heated bodies 'II an'd Il).

Finally, *the head 'chuck and tall i, chuck 4are moved longitudinally'together, .as is vindicated by 'the yarrow' 24."(Fig.:`2),luntil'the vparts 'I0 and II reachfthe sealingposition .shown'iinV Fig. 3. Only the setof "burners, which includes 'burners IB andf, is continued in operation, and the; joint `loetwe'en'bodies I0 and II 'is heated rthereby until the'sealing operation is completed. Then the twobodies are permifttedto lcool. The result is a'vacuumetightassenrbly, as illustrated infFig. 1. "Thesealat;I3"'between the vglass cylinderIIl and the 'metal -sleefve Al2 'of -the lanode assembly 'shown .in Fig. i1 is producedin `the vsame manner and :on the sameor'asimilar lathe.

Th'eX-lfaytube illustrated in Fig. 4 contains `an anodeassembly'fo'fatype whic'irinvolves considerablerdifcultywhen made in'accordance with themanufacturingmethods heretofore available. 'The anodebody 30 is'm'oun'ted .on .a copper stem B'I lwhich `forms 'aflead Vfor sup1c` lyingthe anode current.vv "A sleeve `32 'of nickel-cobalt steell alloy is `solderedfto therfanode -3ll at gSSEby-'means of silver-solder. *The-opposite 1edge't ofthe `sleeve 32 is sealed to a reentrant neck 34 of the glass envelope 35 of the X-raytube.

In constructions of the just-mentioned type, the presence of a silver solder in proximity t0 the edge to be glassed renders `it infeasible to degreas-e and bake the anode structure once the sleeve 32 has been sealed to the anode body. As a result, the vacuum-tight metal-to-glass seal at 33 has often been the cause of defects. By applying the intermediate heat treatment at red heat, i. e.,a relatively moderate temperature, in accordance with the present invention, the just-mentioned diiliculties have been fully overcome.

We have found that the above-described treatment at moderate red heat in a reducing atmosphere is the most essential requirement of our method. It is often preferable to also `apply the above-mentioned polishing treatment with or without a subsequent application of a rag soaked with alcoholic cleaning liquid. However, the hydrogen treatment at about 900 C. is as a rule sufcient to obtain the desired results.

The invention eliminates the diiliculties and eiects which had to be coped with in the past when single or assembled metal parts of alloy steels had to be stored for some time after the application of the hydrogen baking treatment and before applying the nal glassing operation. By virtue of the present invention, the metal sleeves once treated can be used at any time without danger of faulty seals.

It will be obvious to those skilled in the art *that the examples of glass-to-metal seals illus.

trated in the drawing and the auxiliary devices exemplified in the drawing for explaining the method according to the present invention can be modied in various respects, the essential features of our invention residing in the method as defined in the claims following hereafter.

We claim:

1. The method of making on a sealing lathe a seal between a glass body and a previously decarbonized metal structure formed of an iron base alloy with nickel and cobalt and having a coeilcient of expansion similar to that of the glass body, which comprises the steps of placing the decarbonized metal structure on the sealingl lathe in aligned proximity to the glass body ready for immediate interengagement for sealing said glass body to the metal structure, heating the decarbonized structure to a temperature of approximately 900 C. in a reducing atmosphere at the portion to be sealed by applying a hydrogenrich llame for a period of about 3 to 10 minutesy cleaning the structure thus treated while leaving it in said position, and then immediately sealing the structure and the glass body together by applying an oxygen-rich flame.

2. The method of making a seal between a body of boro-silicate glass and a previously decarbonized metal structure formed of an iron .base alloy with nickel and cobalt and having a coefiicient of expansion similar to that of the glass body, which comprises the steps of heat treating the decarbonized metal structure at a temperature of approximately 900 C. fora period of approximately 5 minutes by applying a hydrogen-rich flame, permitting 'the structure to cool, polishing the structure with polishing cloth, cleaning the structure with the -aid of cloth moistened with alcoholic liquid, and then immediat-ely sealing the structure and the glass body together by applying an oxygen-rich flame.

WILLIAM J. KNOCHEL. JENS J. AAKJER..

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

